1. Field of the Invention
The present invention is directed generally to a method and system for controlling the fuel delivery to an engine and, more particularly, to a method and system for controlling the fuel delivery to an engine using adaptive techniques.
2. Description of the Background
In certain applications of internal combustion piston engines, it is desirable to supply an over-rich fuel to air mixture under certain operating conditions. For example, during take-off and climb of an aircraft, the aircraft engine must typically be supplied an over-rich fuel to air mixture. The pilot of the aircraft must manually weaken the mixture when the aircraft reaches low power cruising conditions. The pilot must monitor relevant engine operating parameters via the cockpit instrumentation to periodically adjust the fuel mixture. The fuel mixture must be precisely determined because of the need to ensure adequate fuel supply and to limit engine temperature during the high power, flight safety critical, portions of the aircraft's flight. Thus, the pilot has to devote considerable and constant attention to the instruments to ensure that the fuel flow is reduced during cruise conditions. Typically, the pilot monitors the engine temperature and power reading instruments to set the fuel mixture within pre-defined parameters at which it is assumed that the ideal engine operating point will be attained. The pilot must also monitor the aircraft speed and altitude and ambient temperature and pressure variations, which can affect the required fuel mixture.
When a pilot must devote attention to the aircraft flight path, other aircraft in the vicinity, etc., the pilot may fail to properly weaken the fuel mixture. This results in high levels of exhaust pollutant emissions, carbon buildup on cylinder head components, and, possibly, such high fuel consumption that the planned flight duration of the aircraft may not be achievable. Also, an overly weak fuel mixture can result in reduced engine life due to the overheating of cylinder head components and can also result in a failure of the engine to adequately respond if it were suddenly necessary for the pilot to increase engine power for some flight situation purpose.
In addition to engines which rely on manual pilot intervention to set the fuel mixture, some aircraft engines have electronic engine controls which measure the relevant engine and aircraft operating parameters, digitally process the information, and activate effectors which automatically set the fuel mixture (and other engine functions such as ignition timing) according to preset scheduled values. These systems have the disadvantage in that they rely on predetermined engine characteristic schedules, typically for an average or minimum rated power engine. Thus, they do not take into account engine to engine variations or changes in the desired schedule characteristics with performance changes over the service life of the engine. Thus, under certain conditions, an engine could operate at a fuel mixture as much as five percent away from its ideal stoichiometric fuel mixture.
Thus, there is a need for a system and method for controlling the fuel delivery to an engine which requires no pilot intervention. There is also a need for a system and method for controlling the fuel delivery to an engine which does not rely on predetermined engine characteristic schedules to determine the amount of fuel to deliver to the engine.